Security Assertion Markup Language (SAML) is an open standard that allows identity providers (IdP) to pass authorization credentials to service providers (SP). More info in Wikipedia.
When you specify callback URL in Okta settings use samlcallback.php file name. For instance, if your project resides at https://website.com/myproject, the callback URL will be https://website.com/myproject/samlcallback.php.
Security screen articles:
•CAPTCHA on authentication pages
See also: